The prior art printing process is illustrated in FIG. 1 to which reference is now made. Each individual color page to be printed is prepared on a pre-press device 10. When the designer finishes designing the page, the pre-press device 10 creates four digitized versions 12 of the page, one for each of the four color separations cyan, magenta, yellow and black (C, Y, M, and K). The digitized versions of the page will be known herein as "separation files" 12.
When the designer has finished preparing all of the pages of the printed publication (magazine, newspaper, brochure, etc.) to be printed, he provides the separation files 12 for the entirety of pages to an imposition device 14 (such as provided within the WHISPER I/O Station manufactured by Scitex Corporation Ltd. of Herzlia, Israel) which "imposes" the pages into "signatures" 16. Each signature typically has press marks 18 and eight pages on it where the order that the eight pages are laid out is a function of how the printing press will fold the press sheet after printing. The imposition device 14 produces four data files of the signature, one for each color separation.
The four files representing the signature 16 are provided to a film plotter 20 (such as the DOLEV 800 plotter manufactured by Scitex Corporation Ltd.) which plots each version of the signature 16 onto a film. The result are films 22 of the separations of the signature 16. Blue-line proofs 26 are provided by blue line proofer 26 from films 22. Blue-line proofs 26 is a blue and white print of the signature 16 and is utilized to ascertain that the text is correct, that the placement of the various elements of the pages are correct and aligned and that the general impression of the pages is correct. If it is not, the designer needs to make changes at the pre-press device 10 and the process needs to be repeated.
To determine whether or not the colors to be printed are the desired colors, the films 22 are sent to a Chromalin proofer 26 as produced by Dupont, Delaware, USA for producing a color CHROMALIN proof 29. The film creation process is repeated if the colors are in any way unacceptable.
If the blue-line proof 26 and the color chromalin 29 indicate that there are no problems, the films 22 are provided to a printing press 30 for printing. Each film 22 is utilized to create a press plate and the press plates are placed on separate inking units of the press, onto which the ink of the proper color (cyan, magenta, yellow or black) will be spread.
Since the color varies widely across a page and across a signature, each press inking unit is divided into a plurality of "zones" where each zone has a separate ink flow regulator 32, known as a "zone valve". Each zone valve ensures that the amount of ink which is spread across its zone is compatible with the amount of color desired.
Usually, a press operator initially sets the zone valves 32 by looking at the colors in the Chromalin proof 29. He then prints one sheet with the initial settings, to view the final result. If the colors are smeared in one zone, there is too much ink available and he will have to adjust down the zone valve 32 for the problematic zone. Similarly, if the color is too light, he will have to open up the zone valve 32. The printing process is repeated for another sheet until the desired affect is achieved. After that, the printing press is operated with only spot checks to determine that the ink flow in each zone remains correct.
The Heidelberg Speedmaster 72 printing press, manufactured by Heidelberg Druckmaschinen AG of Germany, has a plurality of zone valves 32 (or fountain keys) which can be controlled directly or remotely. Presses may have 8 to 30 such zone valves.
It will be appreciated that, if the density of a given color is consistent across the zone, the setting for the zone valve 32 is straightforward. However, if the density of the color varies widely over a zone, it is difficult for the press operator to determine how much ink flow to provide.
U.S. Pat. No. 5,128,879 describes a method and apparatus which acquires the zone valve states and adjusts them automatically. The settings of the zone valves are calculated from the color density values provided in the page initially created by the pre-press devices 10. The calculated zone valve settings are forwarded directly to the printing press, without intervention of the press operator.
European Patent Publication 495563 A2 describes an integrated computerized system for use in printing assigned to the common assignees of the present invention. The disclosure of its U.S. counterpart, allowed application No. 07/650,249 now U.S. Pat No. 5,875,288 is incorporated herein by reference. The system includes apparatus for providing and digitally storing at least one digital representation of at least one page. The digital representation is imposed and arranged in accordance with a desired plate layout to define a plate image. Press set-up apparatus then extracts the digital representation and providing press set-up data to a printing press.